Vacuum processing chambers have been used for etching materials from substrates and for deposition of materials onto substrates. The substrates have been semiconductor wafers, for example. In general, accurate processing (and thus high yields of active devices) is expected to occur in a central area of the wafer (i.e., in an active device region). Numerous difficulties are experienced in attempting to accurately process the wafer between the central area and a peripheral edge of the wafer that surrounds the central area on a top, or upper, surface of the wafer that is to be processed to form the devices. Such difficulties are significant enough that an “edge exclusion area” has been defined between the central area and that edge of the wafer. No attempt is made to provide acceptable devices in that edge exclusion area.
Additionally, during the desired processing of the central area, undesired deposits, materials, or process-by-products (collectively “undesired materials”) accumulate or result on the edge exclusion area of the upper surface of the wafer, and on a beveled edge area around the peripheral edge of the wafer, and below the beveled edge area onto a bottom area of an opposite (bottom) surface of the wafer. The edge exclusion area, the beveled edge area, and the bottom area are referred to herein collectively as the “edge environ”. The edge environ is not to be processed to form devices. These undesired materials may generally accumulate on the edge environ. In general, it is desired to keep the edge environ substantially clean, so as to avoid flaking of material particulates that may redeposit back onto the active device regions on the upper surface of the wafer. Such flaking can occur during any number of wafer handling or transport operations, and thus, it is a general desire that the edge environ be periodically cleaned (e.g., etched) to remove the undesired materials from the processed wafers. During a removal, or cleaning, process the edge environ is a region of process (cleaning) performance, and the central area of the active devices is a region of process exclusion.
In view of the foregoing, there are needs for methods and apparatus for removing the undesired materials from only the edge environ and not damaging the central area.